Induction of apoptosis using sphingolipids activates a chloride current inXenopus laevis oocytes

The purpose of this study was to investigate whether the cell shrinkage tha t occurs during apoptosis could be explained by a change of the activity in ion transport pathways. We tested whether sphingolipids, which are potent pro-apoptotic compounds, can activate ionic currents in Xenopus laevis oocy tes. Apoptosis was characterized in our model by a decrease in cell volume, a loss of cell viability, and DNA cleavage. Oocytes were studied using vol tage-clamp after injection with N,N-dimethyl-D-erythrosphingosine (DMS) or D-sphingosine (DS). DMS and DS activated a fast-activating, slowly inactiva ting, outwardly rectifying current, similar to ICl-swell, a swelling-induce d chloride current. Lowering the extracellular chloride dramatically reduce d the current, and the channel was more selective for thiocyanate and iodid e (thiocyanate. iodide) than for chloride. The current was blocked by 5-nit ro-2-(3-phenylpropylamino)-benzoic acid (NPPB) and lanthanum but not by nif lumic acid. Oocytes injected with a pseudosubstrate inhibitor of protein ki nase C (PKC), PKC-(19-31), exhibited the same current. DMS-activated curren t was abolished by preexposure with phorbol myristate acetate. Our results suggest that induction of apoptosis in X. laevis oocytes, using sphingolipi ds or PKC inhibitors, activates a current similar to swelling-induced chlor ide current previously described in oocytes.